As optical disc by which data can be recorded, CD-R, CD-RW, DVD-R, DVD-RW, DVD+R, DVD+RW, and/or DVD-RAM, etc. are known. CD-R, DVD-R and DVD+R are optical discs of the so-called write once type in which the recording layer consists light reactive coloring matter of the organic system so that only one recording operation can be made. In such optical disc of the write-once type, laser beams are irradiated onto organic coloring matter layer to perform thermal reaction of the organic coloring matter layer by energy of the laser beams so that data are recorded. CD-RW, DVD-RW, DVD+RW and DVD-RAM are optical discs of the phase change type in which the recording layer consists of phase change material so that plural recording operations can be made. In such optical disc of the phase change type, laser beams of a predetermined power are irradiated onto the phase change layer to perform transition of the crystal structure of the phase change layer between crystal state and amorphous state so that data are recorded.
In the case where data are recorded with respect to optical discs of the write-once type or the phase change type, if irradiation energy of laser beams given (applied) onto the recording layer is too large or is too small, distortion takes place in shape or edge of formed recording mark so that reproduction characteristic of the recorded data is deteriorated. For this reason, at the time of recording of data, it is necessary to set power of laser beams to a value suitable for write operation. In laser diode which outputs laser beams, output change by, e.g., wavelength or recording speed, etc. with respect to temperature change is very large, and sensitive characteristics of the recording layer have individual differences every optical discs. In such optical discs of the write-once type or the phase change type, trial write area for adjustment of recording power is provided. The disc drive once performs trial write operation of data in the trial write area at the time of recording of data to determine recording power by which sufficient reproduction characteristic of data can be obtained thereafter to conduct recording operation of data.
The physical format of the conventional CD-R (CD-Recordable) indicated at Orange Book Part2, Vol.2, Ver1.0 is shown in FIG. 1.
As shown in FIG. 1, the CD-R is formed so as to take disc shape having diameter of 120 mm. In the information recording area (information area) of CD-R, there are formed, in order, from the inner circumferential side, XAA (extended ATIP Area), PCA (Power Calibration Area), PMA (Program Memory Area), lead-in area, program area and lead-out area.
In the XAA, there are recorded additional information, e.g., coloring matter information of the recording layer, disc maker ID which has manufactured the CD-R, and/or initial value of recording power, etc.
In the PCA, there is recorded trial write data for adjustment of recording power of laser beams. Namely, the PCA is the area where recording power of laser beams in recording data with respect to the program area is set.
In the PMA, address information required at the time of write-once operation of data is temporarily recorded.
In the lead-in area and the lead-out area, there are recorded TOC (Table Of Contents).
In the program area, there is recorded real data.
As described above, in the conventional CD-R, trial write area for adjustment of recording power of laser beams which is called PCA is provided at the disc inner circumferential side.
In the recordable optical discs of the write-once type or the phase change type, data are recorded by, e.g., CLV (Constant Linear Velocity) control system or zone CLV control system, etc. The CLV control system is the system of recording data onto the disc entire surface by constant linear velocity. For this reason, in the CLV control system, as shown in FIG. 2, disc rotational speed (velocity) with respect to the disc radius position linearly becomes small in accordance with shift toward the outer circumferential side. The zone CLV control system is the system in which the recording area of the disc is divided into plural zones in the radial direction to record or reproduce data at constant linear velocity within respective zones so that linear velocities are different from each other between zones. In this zone CLV, linear velocity in the outer circumferential zone is ordinarily high. In the zone CLV control system, as shown in FIG. 3, for example, the disc rotational speed (velocity) with respect to the disc radius position linearly becomes small in accordance with shift toward the outer circumferential side within the zone.
Meanwhile, in the case where data are recorded onto recordable optical disc such as CD-R or CD-RW, etc., the recording sensitivity should be primarily constant at all times on the disc entire surface. For this reason, the optimum value of recording power with respect to the linear velocity ideally becomes constant irrespective of position in the radial direction.
In the case of recording data by the CLV control system, if the recording sensitivity is constant on the disc entire surface, data can be recorded from the innermost circumference to the outermost circumference by recording power (Power[PCA]) determined by writing trial write data into PCA provided at the inner circumferential side as shown in FIG. 4.
In the case of recording data by the zone CLV control system, if the recording sensitivity is constant on the disc entire surface, data can be recorded, by recording power (Power [PCA]) determined by writing trial write data into PCA provided at the inner circumferential side, with respect to the innermost circumferential zone (ZONE 1) as shown in FIG. 5. With respect to other zones, data can be recorded by recording power obtained by multiplying recording power (Power [PCA]) determined by writing trial write data into PCA provided at the inner circumferential side by correction coefficients with respect to respective zones. For example, in the case where three zones (ZONE1, ZONE2, ZONE3) exist, when correction coefficient with respect to the zone 2 is assumed to be WP_Coef—1 and correction coefficient with respect to the zone 3 is assumed to be WP_Coef—1×WP_Coef—2, recording powers with respect to respective zones can be determined in a manner as described below.
Recording power with respect to the zone 1Power [z1]=Power [PCA]
Recording power with respect to the zone 2Power [z2]=Power [PCA]×WP_Coef—1
Recording power with respect to the zone 3Power [z3]=Power [PCA]×WP_Coef—1×WP_Coef—2
As described above, in recordable optical discs such as CD-R or CD-RW, etc., if there results the ideal state where the recording sensitivity is constant on the disc entire surface, data can be recorded on the basis of recording power determined by writing trial write data with respect to one PCA provided at the inner circumferential side irrespective of position in the radial direction (address position where data are recorded) of the disc.
In practice, the recording sensitivity with respect to position in the radial direction (address) of the disc is not constant by factors as described below. For this reason, the optimum value of recording power is changed by the position in the radial direction (address) of the disc.
1) Mechanical characteristic of drive or optical disc such as skew, plane deviation or aberration
2) Temperature/Humidity change and/or aging change of polycarbonate
3) Coating unevenness of organic coloring matter at the time of spin coat, or sputter unevenness of phase change material at the time of deposition
4) Contraction or expansion of base (substrate) at the time of disc molding
5) Relative tilt angle taking place at integrated type CD/DVD common head in which two laser diodes for CD and DVD are mounted
6) Oscillation wavelength change of laser
7) Drive adjustment unevenness or attachment error
Here, the relative tilt angle of 5) refers to relative angle between the optical axis of DVD and the optical axis of CD at optical head common to DVD/CD which is called component head. The component head is caused to be of the configuration comprising two laser diodes of laser diode for DVD and laser diode for CD with respect to one object lens. In such component head common to DVD/CD, speaking ideally, the optical system is designed so that the optical axis of laser beams for CD irradiated from the object lens onto the disc and the optical axis of laser beams for DVD irradiated from the object lens onto the disc are perpendicular to the disc. Namely, design is made so that laser beams are irradiated from the object lens onto the disc in the state where the optical axis of laser beams for CD and the optical axis of laser beams for DVD are in correspondence with each other. However, in practice, the optical axis of laser beams for CD and the optical axis of laser beams for DVD have angle in a relative manner when laser beams are passed through the object lens by influence resulting from unevenness by individual difference of optical parts and/or unevenness of adjustment of the optical axis of respective laser beams for CD and DVD, etc. This angle is called relative tilt angle. In the case where this relative tilt angle is large, light beams are not irradiated in such a manner that either one of optical axes of laser beams for CD, DVD or both optical axes thereof are perpendicular to the disc. As a result, frame aberration, etc. takes place in laser spot. For this reason, recording power of laser beams does not become constant with respect to the disc entire surface so that it changes every position in the radial direction (address) of the disc.
In the case where the optimum value of recording power of laser beams changes in accordance with the position in the radial direction of the disc in a manner as stated above, even if data are recorded onto the disc entire surface by recording power determined by writing trial write data into PCA of the inner circumferential side, reproduction characteristic of recorded data would be deteriorated at recording position remote from the PCA, i.e., at the recording position of the outer circumferential side. For example, in the case of the CLV recording system, the above-described respective factors are greatly influenced according as position becomes close to the outer circumferential side. As a result, differences between recording power determined by writing trial write data into PCA of the inner circumferential side and optimum recording powers at actual respective recording positions become large. In the case of the zone CLV recording system, since recording speed becomes high every zone, differences between the optimum value of recording power of the inner circumferential side and optimum value of recording power of the outer circumferential side are accumulated by the number of zones. As a result, reproduction characteristic of recorded data is further deteriorated.
Particularly, in recent years, realization of high data write speed is being made. In the case where attempt is made to realize such high speed write operation, such error of recording sensitivity that problem does not take place at the conventional low write speed also becomes large to have influence on recording characteristic of data. As a result, when recording power is calculated only by one PCA provided at the inner circumferential side, there is the possibility that data cannot be correctly recorded with respect to the disc entire surface.